1. Technical Field
This disclosure relates to operation of a memory system. More particularly, this disclosure relates to techniques for evaluating a data eye indicating performance characteristics of a memory system.
2. Background Art
As they continue to increase input/output (I/O) data rates, successive generations of memory technologies such as dual data rate (DDR) random access memory (RAM) are increasingly sensitive to the effects of phase difference between signals transmitted on different signal lines. For example, memory system performance may depend on an acceptable phase difference between a data signal DQ and an associated data strobe signal DQS which indicates, for example, a time for the data signal DQ to be read (or not read).
The susceptibility of a memory system to the effects of such signal phase difference may depend on one or more additional parameters of an operating state under which I/O is performed. Evaluation of a memory system's performance under various operating states often includes analysis of a “data eye”—e.g. an area in a graph of operating parameters—in which performance of the memory system in question is considered to be sufficiently reliable.
Techniques for measuring data eye characteristics for a particular memory system have, to date, been limited to various rectilinear approaches—e.g. “eye height” and/or “eye width”. For example, in the case of a data eye in a 2-dimensional plane for two operating parameters, data eye measurements have typically relied upon setting a particular “horizontal” (e.g. phase) value of a first operating parameter, and taking a set of measurements along a range of “vertical” (e.g. voltage) values of the second operating parameter. This measuring of a set of “vertical” values is typically repeated, each set of measurements for a different respective “horizontal” value of the second operating parameter. It is appreciated that these previous practices may use measuring techniques wherein these vertical and horizontal axes are switched.
In addition, analyzing these rectilinear measurements to evaluate a particular operating point of the memory system has typically been limited to evaluating for that operating point an associated “height” of the data eye as measured only in the direction of one of the two operating parameters and/or evaluating for that operating point an associated “width” of the data eye as measured only in the direction of the other one of the two operating parameters. However, reliance on such rectilinear measurement and/or analysis is prone to inefficiency and/or sub-optimal results. For example, an asymmetric or otherwise irregular shape of a data eye may cause regions thereof to escape recognition by measurements which are made only along such horizontal (or vertical) measuring dimensions. Moreover, these irregular data eye features may be inaccurately represented if the data eye is analyzed only in terms of rectilinear squares (or rectangles) having edges parallel to the axes for the operating parameters.
The limitations of using rectilinear measurement techniques may be mitigated by further applying more sophisticated data analysis techniques to the measurement information. However, such analysis techniques require storing all of the rectilinear measurement information for a data eye at one time and then processing the information as a whole. This increases the storage, computational and/or processing time requirements for completing data eye analysis of a memory system's performance characteristics.